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Do Lab-Grown Diamonds Pass a Diamond Tester?
In this guide
Yes. Lab-grown diamonds pass a standard diamond tester every single time, because they are genuine diamonds - pure crystallized carbon, chemically and optically identical to mined stones. A thermal or electrical tester simply reads "Diamond." What it cannot do is tell lab-grown from mined; only specialized lab instruments and the IGI certificate can reveal a diamond's origin.
Why do lab-grown diamonds pass a diamond tester?
A diamond tester does not detect where a diamond came from - it detects what a diamond is. Lab-grown and mined diamonds share the exact same carbon crystal lattice, the same hardness (10 on the Mohs scale), and the same way of moving heat and electricity. Under the probe, they behave identically, so the tester lights up "Diamond" for both.
The confusion usually comes from the word "lab." Shoppers assume a stone grown in a facility must be "fake." It is not. A lab-grown diamond starts as a tiny carbon seed and is grown under the same intense heat and pressure found deep in the earth - just controlled and sped up. The finished crystal sparkles the same and scores the same on every physical test. If you want the full science, our guide on whether lab-grown diamonds are real breaks it down.
How does a diamond tester actually work?
Most handheld testers measure thermal conductivity - how quickly a stone pulls heat away from a warmed probe tip. Diamond moves heat faster than almost any other gem material, so the needle or lights jump straight to "Diamond" for both lab-grown and mined stones. It is a test of material, not origin.
Better "dual" testers add a second check for electrical conductivity. This exists to catch one specific look-alike that also passes the heat test: moissanite. On a thermal-only tester, moissanite can sometimes read as diamond; the electrical probe flags it correctly.
Keep in mind a tester only answers one question: diamond or not diamond. It says nothing about quality, and it cannot separate two real diamonds by origin. Treat it as a quick screen, not a grading tool.
Which stones actually fail a diamond tester?
Simulants - stones that only imitate a diamond's look - are where testers earn their keep. Here is how the common ones respond:
| Stone | Standard thermal tester | What it means |
|---|---|---|
| Lab-grown diamond | Reads "Diamond" | Real diamond |
| Mined diamond | Reads "Diamond" | Real diamond |
| Moissanite | May false-read as diamond | Caught by a dual (electrical) tester |
| Cubic zirconia | Reads "not diamond" | Simulant, fails |
| White sapphire | Reads "not diamond" | Simulant, fails |
So a lab-grown diamond passing the test is not a loophole or a trick. It is the correct result for a real diamond, exactly as a mined stone would read.
Can any tester tell lab-grown from mined?
Not a pocket tester, and not a jeweler's loupe. Because the two are the same material, distinguishing lab-grown from mined requires spectroscopic screening machines that read a diamond's trace-element and growth signatures. These instruments live in professional gem labs like IGI, not at the jewelry counter.
This is worth knowing before you shop: no reseller can "test" a stone in front of you and prove it was mined. If natural origin matters to you, the paperwork is the proof - which is exactly why we offer mined diamonds only as a truly custom commission with full documentation. For a deeper comparison, see lab-grown versus natural diamonds.
Why the IGI certificate is your real proof
Since no tester reveals origin, your genuine assurance is the grading report. Every Signora diamond is IGI-certified, and the certificate states in writing that the stone is laboratory-grown, along with its 4Cs - carat, cut, color and clarity. Many stones are also laser-inscribed with a report number you can verify.
That document does what a $30 pen tester never can. If you are new to grading reports, our explainer on what IGI certification means walks through how to read one. Keep it with your appraisal in a safe place; if you ever resell, insure, or have the piece serviced, that report is the document everyone will ask for.
Do lab-grown diamonds pass at a jeweler or appraiser?
Yes. Bring a lab-grown diamond to any independent jeweler and their tester will read "Diamond," just as it does in the store. An appraiser will measure and grade it as a genuine diamond and can assign a replacement value for insurance. The only difference they will note - drawn from your certificate, not from a tester - is that the stone is laboratory-grown.
That matters for coverage. Insurers write policies based on the IGI report and the appraisal, so a lab-grown stone is fully insurable. Because it costs far less to replace, your annual premium is usually lower too. Whether it is an everyday ring or an anniversary piece, the protection works the same way.
What does this mean when you shop?
It means you can buy a lab-grown diamond with total confidence that it is real - and pay roughly 80 to 95 percent less than a mined diamond of the same certified quality. It will pass any tester a friend, appraiser, or insurer points at it, and it will be graded on the identical scale.
There is also nothing to hide at resale or trade-in. Because a lab-grown diamond tests as a real diamond and comes with its own IGI report, a jeweler evaluates it on the same 4Cs as any other certified stone. You are buying a genuine diamond, documented and verifiable, not an imitation.
Browse certified stones in our diamond finder, or see them set in our engagement rings. Every piece is made to order in solid gold or platinum, never plated.
The bottom line
Lab-grown diamonds pass a diamond tester because they are diamonds, full stop. A tester confirms the material; the IGI certificate confirms the origin. Together they give you certainty at a fraction of the price. Ready to see a real, certified stone for yourself? Start with our loose diamond finder and compare cut, color and clarity side by side.
Questions, answered
Do lab-grown diamonds pass a diamond tester?
Yes, every time. A lab-grown diamond is pure crystallized carbon, so a thermal diamond tester reads it as Diamond exactly like a mined stone. Both share the same hardness of 10 on the Mohs scale and identical heat conductivity. The tester confirms the material is a real diamond; it cannot reveal that the stone was grown in a lab.
Can a jeweler tell a diamond is lab-grown by testing it?
No. A standard tester and a loupe cannot separate lab-grown from mined, because the two are the same material. Only spectroscopic screening machines in professional labs like IGI detect the difference by reading growth signatures. That is why the IGI certificate, which states the stone is laboratory-grown, is your only reliable proof of origin at the counter.
Does moissanite pass a diamond tester?
Sometimes, which is the catch. Moissanite conducts heat well enough to fool a basic thermal-only tester into reading Diamond. That is why dual testers add an electrical-conductivity check, which flags moissanite correctly. Cubic zirconia and white sapphire, by contrast, fail a plain thermal tester outright because they conduct heat far more slowly than a real diamond does.
How can you tell if a diamond is lab-grown?
You rely on paperwork, not a pen tester. Since lab-grown and mined diamonds are physically identical, the certificate is the answer: every IGI report states clearly whether a stone is laboratory-grown. Many diamonds also carry a laser inscription of the report number, often around the girdle, that you can match against the grading document to confirm the stone.
Are lab-grown diamonds real diamonds?
Yes, unequivocally. Lab-grown diamonds are made of the same crystallized carbon as mined diamonds and share every physical, chemical and optical property, including a hardness of 10 on the Mohs scale. They are graded on the identical 4Cs and cost roughly 80 to 95 percent less than a mined diamond of the same certified quality. Only their origin differs.
